Zuckerberg says he won't sell any Facebook shares for 12 months

In an SEC filing late today, Facebook said that founder and CEO Mark Zuckerberg "has no intention to conduct any sale transactions... for at least 12 months."

This comes as Facebook's stock today fell once again, closing down 1.8 percent to a record low of $17.73. That's more than 54 percent off its mid-May IPO price of $38.

Just after the IPO, Zuckerberg sold about $1.1 billion worth of stock, a move the company said was to cover his tax bills. Zuckerberg still holds 504 million Class B shares (those are the ones with extra voting power), which at today's price are worth about $8.9 billion.

The company said that two of its directors -- Marc Andreessen and Donald Graham -- do plan to sell stock, but only to cover their tax liabilities. They don't plan to sell their personal holdings.

In today's filing, Facebook moved up the date when some employees will be able to sell their shares -- to Oct 29 from Nov. 14th. Before today, more than 1 billion shares were free to hit the market on Nov. 14, the biggest of the so-called lockup expirations.